A known injection device intended for a dual injection type internal combustion engine includes a port injector for injecting fuel into an intake port of the internal combustion engine and a cylinder injector for injecting fuel directly into a cylinder. In the injection device for the dual injection type internal combustion engine, either one or both of the port injector and the cylinder injector can be selectively used according to an operating condition of the internal combustion engine. Fuel efficiency and output characteristics can therefore be improved by changing an injection share ratio between injection from the port injector (hereinafter also referred to as “port injection”) and injection from the cylinder injector (hereinafter also referred to as “cylinder injection”) according to the operating condition of the internal combustion engine.
Patent document 1, for example, discloses a fuel injection device of this kind that performs port injection after the engine is started and performs both port injection and cylinder injection simultaneously thereafter. After the engine is started, fuel atomization by cylinder injection may not be promoted because of possible insufficient development of fuel pressure supplied to the cylinder injector. This may cause a deposit of fuel on a cylinder wall. In this fuel injection device, therefore, only the port injection is performed after the engine is started until fuel atomization by the cylinder injection is enabled.
The above-described fuel injection device also estimates an amount of fuel deposited in an intake port up to that point when starting the cylinder injection. The amount of fuel deposited in the intake port is estimated because, after the engine is started, fuel through the port injection may not be atomized due to insufficient warm-up. This can cause the deposit of fuel in the intake port, and the amount of fuel actually burned is possible to be smaller than the amount of port-injected fuel.